This invention concerns aqueous chemical treatment solutions for titanium and its alloys in which a film comprising at least one fluoride of magnesium, calcium, manganese, iron, cobalt, nickel, zinc or molybdenum is chemically formed on the surface of the titanium alloy in order to improve the lubrication properties of the surface when the titanium or titanium alloy is being subjected to cold forming.
Fluoride films of titanium borofluoride, titanium silicofluoride etc. were known in the past as lubrication enhancing chemicaally formed films for use in cold forming work with titanium and its alloys.
These films are soft, thin and have poor adhesion properties but these deficiencies can be improved upon by forming metal fluoride films with manganese, molybdenum, magnesium, calcium, iron, cobalt, nickel and zinc in addition to the titanium fluoride.
An example of treatment compositions for the formation of such films is disclosed in Japanese Patent No. 44-28967 (1969). These treatment compositions for titanium and its alloys consist of an aqueous solution of pH 1.5-4.5 which contain 5-40 grams/liter of fluoride ion and 0.1-5 grams/liter of manganese, molybdenum, zinc, magnesium, calcium, iron, cobalt and/or nickel metal ions.
The fluoride ion which is present in the aqueous solution is provided by the addition of hydrofluoric acid, borofluoric acid, silicofluoric acid or their alkali metal or ammonium salts. The metal ions are provided by the addition of the nitrates, sulfates, chlorides, fluorides, oxides, etc. of the metals manganese, molybdenum, zinc, magnesium, calcium, iron, cobalt and nickel.
The acidic aqueous solutions which have a composition of this type are adjusted to pH 1.5-4.5 with ammonium or caustic soda and heated to a temperature within the range 40.degree.-80.degree. C. and then the titanium or titanium alloy material which has been cleaned by degreasing and acid washing in the usual way is dipped into the solution for some 3-15 minutes whereupon the metal fluoride film for use as a lubrication film is chemically formed on its surface.
The aforementioned metal fluoride films can be used in practice as lubrication films for titanium and its alloys but the adhesion with the base material is still unsatisfactory and there is a problem in that peeling and burning occur during cold forming operations.